This invention relates generally to a clamping device for a seamer and particularly to improvements in a four-bar linkage clamp adapted to position plates edgewise for seam welding.
There are many different clamping devices available for seam welding plate material having the same general purpose as the present device; they can be conveniently considered in terms of two broadly defined groups, namely those referred to as paddle clamps and those referred to as four-bar linkage clamps. In the case of the paddle clamps, the clamping force is applied to each workpiece by a radial arm and the horizontal component of this force tends to urge the workpieces apart. In the case of the four-bar linkage clamps the linkage can be arranged so that the horizontal component of the clamping force tends to urge the workpieces together which is a desirable feature.
Unfortunately, clamping devices using a four-bar linkage system tend to be complicated partly because they must be manufactured to close tolerances so that the individual clamps act in concert. This factor tends to increase the expense of such devices prohibitively. Moreover, in the more common four-bar linkage devices, the pressure levers of the individual clamping units are not readily removable because they are attached to common horizontal pivot shafts of considerable length. Removal of individual clamping units is an advantage because it provides a simple means of avoiding local obstructions on the workpiece such as pimples. Inflatable flexible hoses are the most common medium used for applying the clamping force in seamers. A disadvantage of the common type of four-bar linkage lies in the application of the clamping force from the flexible hose to the clamping member through the relatively indirect medium of a bell crank pressure lever, the flexible hose being disposed between said lever and the sidewall of the reaction beam.
In addition to the above, another disadvantage of known four-bar linkage devices lies in the difficulty of adjusting the location of the linkage pivot points to vary location of the points of pressure to suit workpiece plates of varying thickness. This is a particularly serious problem when longitudinal pivot shafts are used to mount a large number of individual clamping units to an overhead beam because of the common existence of longitudinal misalignment of such overhead beams caused during fabrication.
The present clamping device overcomes these and other problems in a manner not disclosed in the known prior art.